Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
Nat Commun. 2013;4:1678. doi: 10.1038/ncomms2689.
Light-driven proton-pumping rhodopsins are widely distributed in many microorganisms. They convert sunlight energy into proton gradients that serve as energy source of the cell. Here we report a new functional class of a microbial rhodopsin, a light-driven sodium ion pump. We discover that the marine flavobacterium Krokinobacter eikastus possesses two rhodopsins, the first, KR1, being a prototypical proton pump, while the second, KR2, pumps sodium ions outward. Rhodopsin KR2 can also pump lithium ions, but converts to a proton pump when presented with potassium chloride or salts of larger cations. These data indicate that KR2 is a compatible sodium ion-proton pump, and spectroscopic analysis showed it binds sodium ions in its extracellular domain. These findings suggest that light-driven sodium pumps may be as important in situ as their proton-pumping counterparts.
光驱动质子泵视紫红质广泛分布于许多微生物中。它们将太阳能转化为质子梯度，作为细胞的能量来源。在这里，我们报告了一种微生物视紫红质的新功能类别，即光驱动的钠离子泵。我们发现海洋黄杆菌 Krokinobacter eikastus 拥有两种视紫红质，第一种 KR1 是典型的质子泵，而第二种 KR2 则向外泵出钠离子。视紫红质 KR2 也可以泵出锂离子，但当遇到氯化钾或更大阳离子的盐时，它会转化为质子泵。这些数据表明 KR2 是一种兼容的钠离子-质子泵，光谱分析表明它在细胞外结构域结合钠离子。这些发现表明，光驱动的钠离子泵在原位可能与质子泵一样重要。
